Process for preparing 6-aminocapronitrile

ABSTRACT

The invention concerns a process for the preparation of 6-aminocapronitrile or 6-aminocapronitrile-hexamethylene diamine mixtures by: a) reacting 5-formylvaleronitrile with ammonia and hydrogen in the presence of hydrogenation catalysts selected from the group consisting of metals or metal compounds rhenium, copper and elements of group VIII of the periodic table of elements, a hydrogenation discharge product being obtained; and b) extracting from the hydrogenation discharge product 6-aminocapronitrile and optionally hexamethylene diamine, provided that the hydrogenation catalyst does not contain copper, nickel or copper and nickel as it&#39;s only components.

This Application is A 371 of PCT/EP97/03981 filed on Jul. 23, 1997.

DESCRIPTION

The present application relates to a process for the preparation of6-aminocapronitrile or 6-aminocapronitrile/hexamethylene diaminemixtures starting from 5-formylvaleronitrile.

EP-A 11,401 describes the reductive amination of δ-cyanovaleraldehyde toproduce hexamethylene diamine. According to Example 4 of the citedapplication a mixture containing 60% of δ-cyanovaleraldehyde was causedto react with ammonia and hydrogen at a temperature of 100° C. and ahydrogen pressure of 140 bar in the presence of Raney nickel over aperiod of two hours, the conversion (based on the δ-compound) being only25%. The low degree of conversion demonstrates that the aminatinghydrogenation of an aldehyde group and the hydrogenation of a nitrilegroup in the same molecule to form a diamine represent a difficulthydrogenation problem. Furthermore the formation of 6-aminocapronitrileis not described. Furthermore the on-stream time of the catalyst used isunsatisfactory for economic exploitation.

U.S. Pat. No. 2,777,873 reveals that it is possible to perform aminatinghydrogenation on 5-formyl valerate using ammonia and hydrogen in thepresence of nickel, cobalt, iron, platinum, or palladium catalysts atfrom 100° to 160° C. and under pressures ranging from 1 to 1000atmospheres to produce 6-aminocaproates. EP-A 376,121 describes thisreaction also for ruthenium catatysts, the process being carried out attemperatures ranging from 80° to 140° C. and under pressures rangingfrom 40 to 1000 bar.

Cobalt, copper, and rhenium catalysts are suitable for the hydrogenationof adipodinitrile to hexamethylene diamine in the presence of ammonia,as stated in U.S. Pat. No. 3,461,167, column 3, lines 66 to 74. Theprocess is preferably operated at from 70° to 170° C. and from 300 to7000 psi. According to U.S. Pat. No. 3,471,563 ruthenium catalysts canalso be used for this reaction.

Thus Group VIIIb elements hydrogenate both nitrile and aldehyde groupsto produce amino groups.

It is thus an object of the present inventionto provide a process whichmakes it possible to prepare, starting from 5-formylvaleraldehyde,either 6-aminocapronitrile or a mixture of 6-aminocapronitrile andhexamethylene diamine at a very high conversion rate. A particularobject of the invention is to find a process which guarantees longon-stream times of the catalysts.

Accordingly, there has been found a process for the preparation of6-aminocapronitrile or a mixture of 6-aminocapronitrile andhexamethylene diamine, in which

a) 5-formylvaleronitrile is caused to react with ammonia and hydrogen inthe presence of hydrogenation catalysts selected from the groupconsisting of metals or metal compounds of rhenium, copper and GroupVIIIb elements, giving a hydrogenation effluent, and

b) 6-aminocapronitrile and possibly hexamethylene diamine is/areisolated from the hydrogenation effluent,

provided that the hydrogenation catalyst does not contain copper,nickel, or copper and nickel as sole components.

The starting compound used in the process of the invention is5-formylvaleraldehyde. The patent literature reveals a number ofpossibilities for the preparation of 5-formylvaleronitrile:

WO 94/26688 describes a process, in which

(a) internal substituted olefins are isomerized to form terminalolefins,

(b) the terminal olefins are preferably hydroformylated in the presenceof the internal olefins,

(c) the products of the hydroformylation are separated and

(d) the internal olefins are recycled to the isomerization stage.

In claim 3 of the cited WO 94/26688 there are claimed nitrile-containingolefins. The hydroformylation catalysts used arerhodium/triphenylphosphine systems, in which the triphenylphosphine isrendered soluble in water by suitable functional groups.

WO 95/18783 describes the hydroformylation of internalnitrile-containing olefins using water-soluble platinum catalysts.

EP-A 11,401 also reveals that it is possible to cause 3-pentenenitrileto react with carbon monoxide and hydrogen under pressure in thepresence of a cobalt catalyst. During this procedure there is formed amixture of isomeric formylvaleronitriles and the alcohols correspondingto the aldehyde group.

5-Formylvaleronitrile is caused, in the process of the invention, toreact at temperatures ranging from 40° to 150° C., advantageously from50° to 140° C. and more advantageously from 60° to 130° C., andpressures ranging from 2 to 350 bar, advantageously from 20 to 300 barand more advantageously from 40 to 250 bar, with ammonia and hydrogen inthe presence of hydrogenation catalysts in a first step (stage a))giving a hydrogenation effluent.

The reaction is carried out preferably in liquid ammonia acting assolvent, in which case the ammonia simultaneously serves as reactant.The amount of ammonia is usually from 1 to 80 mol and in particular from10 to 50 mol of ammonia per mole of 5-formylvaleronitrile. It may alsobe advantageous to use, in addition to ammonia, a solvent inert underthe reaction conditions, such as an alcohol, ester, ether, orhydrocarbon, in which case a ratio by weight of solvent to5-formylvaleronitrile ranging from 0.1:1 to 5:1 and preferably from0.5:1 to 3:1 is generally used. Alcohols such as methanol and ethanolare particularly preferred.

The amount of hydrogen employed is usually such that the molar ratio ofhydrogen to 5-formylvaleronitrile ranges from 1:1 to 100:1 andpreferably from 5:1 to 50:1.

The catalysts used in the process of the invention are hydrogenationcatalysts, which are selected from the group consisting of metals ormetal compounds of rhenium, copper, and the Group VIlb elements(referred to below as "hydrogenating metals"), preferably iron, cobalt,nickel, ruthenium, rhodium, palladium, osmium, iridium, and platinum,more preferably ruthenium, cobalt, palladium, and nickel, provided thatthe hydrogenation catalyst does not contain copper, nickel, or copperand nickel as sole components.

The catalysts used in the process of the invention can be solidcatalysts or supported catalysts. Examples of suitable support materialsare porous oxides such as aluminum oxide, silicon dioxide, aluminumsilicates, lanthanum oxide, titanium dioxide, zirconium dioxide,magnesium oxide, zinc oxide and zeolites and also activated charcoals ormixtures of said compounds.

The catalysts can be used as fixed-bed catalysts for ascending ordescending reactants or as suspension catalysts. The space velocity usedis preferably in the range of from 0.1 to 2.0 and more preferably from0.3 to 1 kg of 5-formylvaleronitrile per liter of catalyst per hour.

Another possibility is to use compounds of the aforementioned metals ashomogeneously dissolved hydrogenation catalysts.

In a preferred embodiment, the homogeneously dissolved catalysts canfurthermore contain from 0.01 to 25 wt % and preferably from 0.1 to 5 wt%, based on the total amount at hydrogenating metals (calculated aselements), of at least one promotor based on a metal selected from thegroup consisting of copper, silver, gold, manganese, zinc, cadmium,lead, tin, scandium, yttrium, lanthanum and the lanthanide elements,titanium, zirconium, hafnium, chromium, molybdenum, tungsten, vanadium,tantalum, antimony, bismuth, and aluminum, and also doped by from 0.01to 5 wt % and preferably from 0.1 to 3 wt %, based on the hydrogenatingmetals (calculated as elements) of a compound based on an alkali metalor an alkaline earth metal, preferably alkali metal and alkaline earthmetal hydroxides such as lithium hydroxide, sodium hydroxide, potassiumhydroxide, rubidium hydroxide, cesium hydroxide and more preferablylithium hydroxide.

The catalysts used in the process of the invention may be, eg, so-calleddeposited catalysts. These catalysts can be prepared by precipitatingtheir catalytically active components from salt solutions thereof, inparticular from the solutions of their nitrates and/or acetates, forexample by the addition of alkali metal and/or alkaline earth metalhydroxide and/or carbonate solutions, eg, difficultly solublehydroxides, hydrated oxides, basic salts or carbonates, and then dryingthe resulting precipitates and converting them to the correspondingoxides, mixed oxides and/or mixed-valence oxides by calcination attemperatures generally ranging from 300° to 700° C. and in particularfrom 400° to 600° C., which oxides are usually reduced by treatment withhydrogen or hydrogen-containing gases usually at from 50° to 700° C. andin particular from 100° to 400° C. to give the respective metals and/oroxidic compounds of a lower degree of oxidation and are thus convertedto the actual catalytically active form. Reduction is usually continueduntil no more water is formed.

In the preparation of deposited catalysts which include a supportmaterial the precipitation of the catalytically active components cantake place in the presence of the desired support material.Alternatively and advantageously, however, the catalytically activecomponents can be simultaneously precipitated with the support materialfrom appropriate salt solutions. In the process of the inventionhydrogenation catalysts are preferably used which contain thehydrogenation-catalyzing metals or metal compounds deposited on asupport material. Apart from the aforementioned deposited catalystscontaining the catalytically active components in addition to a supportmaterial, suitable support materials for the process of the inventionare generally those onto which the hydrogenation-catalyzing componentshave been applied, eg, by impregnation.

The method of applying the catalytically active metals to the support isusually not crucial and can be effected in a variety of ways. Thecatalytically active metals can be applied to these support materialsfor example by impregnation with solutions or suspensions of the saltsor oxides of the respective elements followed by drying and reduction ofthe metal compounds to the metals or compounds of a lower degree ofoxidation by means of a reducing agent, preferably hydrogen or a complexhydride.

Another possibility for the application of the catalytically activemetals to said supports consists in impregnating the support withsolutions of thermally readily decomposable salts, eg, nitrates orthermally readily decomposable complex compounds, for example carbonylor hydride complexes of the catalytically active metals, and heating thethus impregnated support to temperatures usually ranging from 300° to600° C. for the purpose of thermal disintegration of the adsorbed metalcompounds. This thermal disintegration is preferably carried out under ablanket of protective gas. Suitable protective gases are, for example,nitrogen, carbon dioxide, hydrogen, or a noble gas.

Furthermore the catalytically active metals can be deposited onto thecatalyst support by vapor deposition or flame spraying. The weight ofcatalytically active metals in these supported catalysts istheoretically insignificant for the successful operation of the processof the invention. It will be obvious to the person skilled in the artthat higher contents of catalytically active metals in these supportedcatalysts will usually provide higher space-time yields than lowercontents. Supported catalysts are generally used in which the content ofcatalytically active metals is from 0.1 to 90 wt % and preferably from0.5 to 40 wt %, based on the entire catalyst.

Since these contents are specified with respect to the entire catalystincluding its support material, but different support materials havevery different specific weights and specific surface areas, it may bepossible to use lower or greater contents, however, without having anydisadvantageous effect on the results achieved by the process of theinvention. Of course it is possible to apply a number of catalyticallyactive metals to the said support material. Furthermore, thecatalytically active metals can be applied to the support by, forexample, the processes described in DE-A 2,519,817, EP-A 1,477,219 andEP-A 285,420. In the catalysts described in said specifications thecatalytically active metals are present in the form of alloys, which canbe produced by thermal treatment and/or reduction of the supportmaterials after treatment thereof with a salt or complex of said metalsby, say, impregnation.

Activation of both the deposited catalysts and the supported catalystscan, if desired, take place in situ at the commencement of the reactionby means of the hydrogen present, but preferably these catalysts areactivated before use.

From the hydrogenation effluent obtained in stage a) of the process ofthe invention there is isolated, by usual methods such as distillation,6-aminocapronitrile, optionally together with hexamethylene diamine(stage b)).

In a preferred embodiment, the isolation of 6-aminocapronitrile and, ifdesired, hexamethylene diamine in stage b) is preceded by the separationof ammonia and hydrogen and, if desired, the catalyst.

In another preferred embodiment 5-formylvaleronitrile is first of alltreated at temperatures ranging from 40° to 150° C. with ammonia (firststage) giving an ammoniacal effluent. This can take place for example inan upstream reactor. This reaction can take place in the absence of or,preferably, in the presence of an acidic, homogeneous or heterogeneouscatalyst. In this case the space velocity (using heterogeneouscatalysts) is usually from 0.1 to 2.0 kg of 5-formylvaleronitrile perliter of catalyst per hour.

The ammoniacal effluent can then, if desired, be freed from the acidcatalyst (second stage).

In a third stage the ammoniacal effluent or the ammoniacal solution iscaused to react with ammonia and hydrogen in the presence ofhydrogenation catalysts selected from the group consisting of metals ormetal compounds of the elements copper and rhenium and Group VlIlbelements, giving a hydrogenation effluent, this process usually beingcarried out in the same way as the process described above. The processis followed by isolation of 6-aminocapronitrile and optionallyhexamethylene diamine from the hydrogenation effluent by known methods.

The acid catalysts used can be for example zeolites in the H form, acidion exchangers, heteropoly acids, acidic and superacidic metal oxides,which may optionally be doped with sulfate or phosphate, and inorganicor organic acids.

Examples of suitable zeolites are representatives of the mordenite groupor porous erionite- or chabasite-type zeolites or faujasite-typezeolites, eg, Y-type, X-type, or L-type zeolites. This group alsoincludes the so-called "ultra-stable" faujasite-type zeolites, iedealuminated zeolites.

Particularly advantageous zeolites are those having a pentasil structuresuch as ZSM-5, ZSM-11, and ZMB-10. All of these have as basic buildingblock a five-membered ring composed of SiO₂ tetrahedrons. They arecharacterized by a high SiO₂ /Al₂ O₃ ratio and also by pore sizessituated between those of A-type zeolites and those of X-type or Y-typezeolites.

The heteropoly acids used in the process of the invention are inorganicpoly acids, which, unlike isopoly acids, possess at least two differentcentral atoms. Examples thereof are dodecatungstophosphoric acid H₃ PW₁₂O₄₀ •H₂ O and dodecamolybdophosphoric acid H₃ PMo₁₂ O₄₀ •H₂ O.Theoretically, all of the catalysts and catalyst combinations describedin EP-A 158,229 can be used.

Preferred heteropoly acids are heteropoly acids of molybdenum ortungsten with phosphoric acid, telluric acid, selenic acid, arsenic acidor silicic acid, in particular with phosphoric acid.

Some of the protons of the heteropoly acids can be replaced by metalions, of which alkali metal and alkaline earth metal ions are preferred.

Preferred acid ion exchangers are, eg, cross-linked polystyrenescontaining sulfonic acid groups.

Acid metal oxides are for example SiO₂, Al₂ O₃, ZrO₂, Ga₂ O₃, PbO₂, Sc₂O₃, La₂ O₃, TiO₂, SnO₃, etc. or combinations of individual oxides. Toincrease their acidity, the oxides can by treated with mineral acidssuch as sulfuric acid, if desired.

Suitable acids are for example mineral acids such as sulfuric acid andphosphoric acid and also organic acids such as sulfonic acids.

Suitable superacidic metal oxides are, eg, sulfate-doped ZrO₂ or ZrO₂containing molybdenum or tungsten.

In another preferred embodiment the hydrogenation is carried out over ahydrogenating metal, applied to one of said oxidic supports. Followingthe removal of excess hydrogen and, optionally, of the catalyst, thehydrogenation effluent is preferably worked up to 6-aminocapronitrileand possibly hexamethylene diamine by fractional distillation.

The process of the invention yields 6-aminocapronitrile at very goodconversion rates and good yields and selectivities. It is also possible,by varying the temperature and space velocity, to obtain mixtures of6-aminocapronitrile and hexamethylene diamine. Relatively hightemperatures and low space velocities favor the formation ofhexamethylene diamine, whilst lower temperatures and high spacevelocities favor the formation of capronitrile.

6-Aminocapronitrile and hexamethylene diamine are important fiberprecursors. 6-Aminocapronitrile can be cyclisized to caprolactam, theintermediate for the preparation of nylon 6. Hexamethylene diamine ismostly caused to react with adipic acid to form the so-called AH salt,the intermediate for nylon 6.6.

EXAMPLES Example 1

In an autoclave having a capacity of 300 ml and equipped with a samplingsluice (material HC 4) there were placed 11 g of 5-formylvaleronitrileand 3 g of Ru (3%) on Al₂ O₃ (4 mm extrudates) under protective gas(argon). The autoclave was then sealed and 150 ml of NH₃ were forced in.Thorough mixing was effected using a magnetic stirrer. After heating to80° C. (autogenous pressure: ca. 39 bar) the mixture was kept at 80° C.for a further 2 hours and then the overall pressure was raised, withhydrogen, to 70 bar. The pressure of 70 bar was maintained by constantlyforcing in more hydrogen. After 25 hours, the autoclave wasdepressurized and the hydrogenation effluent analyzed by gaschromatography. The products formed comprised 73% of 6-aminocapronitrileand 12% of hexamethylene diamine. The conversion was 100%.

Example 2

In the autoclave described in Example 1 there were placed 20 g of5-formylvaleronitrile and 3 g of Pd (2%) on Al₂ O₃ powder and 0.41 g oflithium hydroxide under protective gas (argon). The autoclave was thensealed and 140 ml of NH3 were forced in. The mixture was stirred using amagnetic stirrer and was heated to 100° C. and the overall pressureraised to 80 bar by forcing in hydrogen and then kept at this value bycontinuous replenishment with hydrogen. After a period of 23 hours theautoclave was depressurized and the hydrogenation effluent analyzed bygas chromatography. The products formed comprised 59.01% of6-aminocapronitrile and 5.1% of hexamethylene diamine (conversion 100%).

Example 3

The cobalt catalyst used in this example (23% of Co/Al₂ O₃, 4 mmextrudates) was activated before use for the preparation of6-aminocapronitrile by treatment under a stream of hydrogen for 2 hoursat 250° C.

In the autoclave described in Example 1 there were placed 32 g of5-formylvaleronitrile and 10 g of cobalt catalyst under argon. Theautoclave was then sealed and 130 ml of ammonia were forced in. Themixture was stirred using a magnetic stirrer and was heated to 100° C.and the overall pressure raised to 100 bar by forcing in hydrogen andthen kept at this value by continuous replenishment with hydrogen. Aftera period of 20 hours the autoclave was depressurized and thehydrogenation effluent analyzed by gas chromatography. The productsformed comprised 56% of 6-aminocapronitrile and 6% of hexamethylenediamine (conversion 100%).

Preparation of 6-Aminocapronitrile

SUMMARY

The preparation of 6-aminocapronitrile or6-aminocapronitrile/hexamethylene diamine mixtures, in which

a) 5-formylvaleronitrile is caused to react with ammonia and hydrogen inthe presence of hydrogenation catalysts selected from the groupconsisting of metals or metal compounds of rhenium, copper, and GroupVIIIb elements, giving a hydrogenation effluent, and

b) from the hydrogenation effluent there is isolated 6-aminocapronitrileand possibly hexamethylene diamine, provided that the hydrogenationcatalyst does not contain copper, nickel, or copper and nickel as solecomponents.

What is claimed is:
 1. A process for the preparation of6-aminocapronitrile, whereina) 5-formylvaleronitrile is reacted withammonia and hydrogen in the presence of a hydrogenation catalystselected from the group consisting of metals or metal compounds of iron,cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium andplatinum, giving a hydrogenation effluent, and b) from the hydrogenationeffluent there is isolated 6-aminocapronitrile,provided that thehydrogenation catalyst does not contain nickel as sole component.
 2. Theprocess defined in claim 1, wherein the hydrogenation catalyst isselected from the group consisting of metals or metal compounds ofruthenium, cobalt, palladium and nickel.
 3. The process defined in claim1, wherein excess ammonia and hydrogen are removed in stage b) prior tothe isolation of 6-aminocapronitrile.
 4. The process defined in claim 3,wherein the catalyst is also removed in stage b).
 5. The process definedin claim 1, further comprisingfirst treating 5-formylvaleronitrile withammonia to give an ammoniacal effluent, and thereafter reacting saidammoniacal effluent in stage a).
 6. The process defined in claim 5,wherein said treatment of 5-formylvaleronitrile is carried out in thepresence of an acid catalyst.
 7. The process defined in claim 6, whereinsaid acid catalyst is removed from the ammoniacal effluent prior tostage a).
 8. The process defined in claim 1, wherein the6-aminocapronitrile is isolated as a mixture with hexamethylene diamine.9. The process defined in claim 1, wherein stage a) is carried out at atemperature of from 40 to 150° C.
 10. The process defined in claim 1,wherein stage a) is carried out at a pressure of from 2 to 350 bar. 11.The process defined in claim 1, wherein stage a) is carried out inliquid ammonia.
 12. The process defined in claim 1, wherein stage a) iscarried out in an inert solvent.
 13. The process defined in claim 1,wherein the molar ratio of hydrogen to 5-formylvaleronitrile is from 1:1to 500:1.
 14. The process defined in claim 5, wherein the5-formylvaleronitrile is treated with ammonia at a temperature of from40 to 150° C.